In wire cut electric discharge machines where an electric discharge is produced at an electric discharge machining region between a wire electrode (hereinafter referred to as wire) and a workpiece to perform a machining operation while the wire is conveyed along a wire transport path, a machining fluid is supplied to the electric discharge machining region to remove the heat and swarf produced in the region and to establish an appropriately insulated state between the wire and the workpiece. The machining fluid is also supplied to a worktable on which the workpiece is placed, and other parts (hereinafter referred to as worktable), to cool them so that deterioration in the machining precision due to thermal deformation of the worktable can be prevented.
To this end, electric discharge machines are provided with a machining fluid circulating apparatus. Conventional machining fluid circulating apparatuses have a water tank for storing water as the machining fluid, and the water is pressurized by a pump disposed in a first pipe connected to the water tank, to be injected toward the electric discharge machining region and the worktable from a nozzle, and a sprinkler respectively connected to second and third pipes branching off from the first pipe. To allow adjusting of the amount of water supplied to the electric discharge machining region in accordance with a target machining speed and target machining precision, which are set in dependence on machining types such as rough machining, finish machining, etc., the quantity of discharge of the pump or the valve opening of a flow control valve arranged in the first pipe is adjusted.
Consequently, in response to the opening/closing of the flow control valve for controlling the amount of water supplied to the electric discharge machining region, the amount of water supplied to the worktable through the sprinkler is also varied in proportion to the amount of water supplied to the electric discharge machining region. As a result, the temperature of the worktable is varied each time the valve opening of the flow control valve is adjusted, thus causing deformation of the worktable and hence deformation of the workpiece. This results in a deviation in the electric discharge machining position. In such a case, it is difficult to carry out an electric discharge machining with the required precision. Particularly, when carrying out a rough machining and then a finish machining several times at different machining speeds to attain a machining precision of the submicron order, with the amount of water supplied to the electric discharge machining region varied to different required amounts in individual machining steps, the amount of water supplied to the worktable is varied between the machining steps and the worktable or even the workpiece may be deformed, thus causing a deviation in the machining position and making it difficult to achieve the required machining precision.
To eliminate the above inconveniences, a machining fluid circulating apparatus having independent pumps for exclusively supplying the machining fluid to the electric discharge machining region and the worktable, respectively, is conventionally used, but this type of apparatus is high in cost.